| In recent years,bendable and stretchable flexible electronic devices have attracted extensive attention due to their great potential in the fields of human health monitoring and conformal integration.The realization of wireless communication and energy supply of extensible flexible electronic devices is of great significance to improve the application convenience of the devices and broaden the application scenarios.To achieve this goal,the design and preparation of small size,light weight,good flexibility of the miniaturized antenna is the key point.Based on the basic monopole antenna theory and frequency independent antenna theory,the design and fabrication of deformable radio frequency antenna for flexible electronic devices are systematically studied.Firstly,the return loss and the radiation pattern of monopole antenna operating in the 2.5GHz frequency band with the same length and different shape are simulated in this paper.Then the relationship between antenna deformation after stretching and antenna characteristics is analyzed.The results show that the working frequency of the antenna decreases after stretching,and the greater stretchable of antenna is,the greater the frequency reduction will be.While,there is no significant change in the radiation pattern characteristics after the tensile strain is applied.Secondly,based on the theory of frequency independent antenna,a flexible Archimedean-equiangular spiral antenna is designed by incorporating the equiangular spiral structure into the Archimedes spiral antenna structure.The simulation results show that by embedding the equiangular spiral structure before the Archimedes spiral structure,the input impedance of the whole antenna can be reduced to 75? while the tensile property of the antenna can be realized,which solves the problem that flexible antenna cannot use balun and other hard impedance converter to achieve impedance transformation.Furthermore,the flexible Archimedean-equiangular spiral antenna is fabricated by the flexible copper-coated PI(polyimide)plate and PDMS(polydimethylsiloxane).The relationship between the performance and shape variables of the antenna in different deformation modes was tested by using a stretching platform and a balloon after fabrication.The test results show that when the antenna is horizontally stretched by 7.9%,the working frequency range has no obvious change compared with that without deformation.And when the antenna is attached to the balloon and generates a shape variable of 10 mm in the direction of +Z,the working frequency range has also no obvious change compared with that without deformation,which indicates that the antenna can maintain stable operating frequency range from 1.5GHz to 4.5GHz in both deformation modes.The effects of tensile deformation on antenna directivity,gain and axial ratio are analyzed by electromagnetic simulation software and finite element simulation software at the same time.The results show that the directivity of the antenna in the +Z direction is enhanced,while that in the-Z direction is decreased,and the antenna gain can remain stable lager than 3.5dB before and after the deformation.The axial ratio still meets the requirement of circular polarization,indicating that the tensile deformation has little influence on the antenna designed in this paper.Above all,based on the basic monopole antenna theory and frequency independent antenna,this paper discusses the relation between the deformation of antenna and the characteristics of monopole antenna under tensile action,and designs and fabricates a flexible Archimedean-equiangular spiral antenna.The performance parameters such as working frequency,radiation patterns and gain of Archimedean-equiangular spiral antenna were measured and calculated.Test and simulation results both show that the designed antenna can reduce the input impedance while achieving tensile deformation by embedding equiangular spiral structure before Archimedean spiral antenna structure.It avoids the use of rigid impedance converter in the antenna and ensures that the performance parameters of antenna can remain stable after mechanical deformation. |
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